1. Field of the Invention
This invention relates generally to the techniques for devices for delivering medicaments to selected sites in tissue. Specifically, this invention relates to an apparatus for securingly positioning a drug or medication delivering catheter after the catheter is positioned in the brain, spinal epidural space, the intrathecal space or in a peripheral nerve application or in other tissue.
2. Description of the Related Art
Medication delivery to the brain, spinal cord, cerebrospinal fluid or other tissue throughout the body is useful in treating many maladies, diseases and illnesses. Through the use of an implantable pump and catheter, precise drug doses can be directly delivered to the area of interest to treat the malady, disease or illness or its symptoms.
Controlled placement of drug delivering catheters in the position of interest is highly desirable. This allows highly concentrated drugs or other medicaments to be delivered to a specific site where, because the drug or medicament is highly concentrated, the therapeutic effect will be maximnized. Further, because only a small amount of such highly concentrated drug or medicarnent is needed at the site to be therapeutically beneficial, side effects from receiving relatively large doses of the drug orally or intravenously are minimized.
In view of the desirability of placing the highly concentrated drug or medicament at a specific site, movement of the catheter from its desired position is highly problematic. This is a problem known as xe2x80x9cdislodgmentxe2x80x9d. Dislodgment means that the distal tip of the catheter is moved enough from its desired position for the therapy to be affected. For some therapies, for example, intrathecal administration of drugs to the spinal cord, movement on the order of 0.5 inch or less may cause a noticeable decrease in therapy. For others, such as when a catheter is implanted in the intrathecal space of the spinal cord, the catheter must exit the intrathecal space to cause a change in therapy. This can be as much as 8 inches.
It is rare for the anchor to move relative to the tissue it is attached to. It is much more likely for the catheter to move relative to the anchor (slip through). Where the catheter is implanted in the spine, an anchor is typically placed outside the spine and is anchored to a ligament. In this case, it is not uncommon for the catheter to exit the spine and xe2x80x9cbunch upxe2x80x9d just distal to the anchor between the anchor and the entrance to the spine.
Dislodgment causes the highly concentrated drug or other medicament to not be delivered to the desired location. As a result, the desired therapeutic effect is not achieved. In addition, applying the highly concentrated drug or medicament to another site may produce undesired effects. Therefore, dislodgment is a condition to be avoided.
There are currently several ways physicians attempt to solve the problem of dislodgment. One way is to suture the catheter to tissue to xe2x80x9canchorxe2x80x9d the catheter to the tissue. A problem with this approach is that often the suture cuts through or occludes the catheter thereby disabling the catheter. This prevents the desired drug or medicament from passing to the distal end of the catheter to be delivered to the target site. In addition, the drug or medicament then leaks out of the cut area where it may possible cause undesirable effects.
Another way to solve the dislodgment problem is to place an xe2x80x9canchorxe2x80x9d around the catheter and then secure the anchor to tissue. In this way, the anchor prevents the catheter from moving relative to the anchor and the anchor itself is prevented from moving relative to tissue because the anchor is securely fastened to the tissue.
An example of such an anchor is shown in FIGS. 1-4 labeled generally 2. The anchor 2 has a tubular body 4 and a pair of opposed wings 6. Body 4 has a central channel 8. Central channel 8 is typically sized to be the same diameter as the outer diameter of a catheter 14 that is to be secured by the anchor 2. Body 4 often has a longitudinal slit 10 that extends entirely through body 4 along the entire length of body 4.
The wings 6 each have an eyelet 12. In use, a catheter 14 is placed through slit 10 into channel 8. Because of the tight tolerance in the diameter of central channel 8 and the outer diameter of catheter 14, it is very difficult if not impossible to thread catheter 14 through channel 8. Thereafter, anchor 2 is moved to the desired position. Wings 6 are pinched together toward slit 10. A suture 16 is placed through eyelets 12 and tissue 18 to secure the catheter 14 in the anchor 2 and anchor 2 to tissue 18 (FIG. 4).
A problem with this design for anchor 2 is that as wings 6 are brought together, the material of body 4 develops hoop stresses. Hoop stresses are the stresses that develop as a tightening force is applied to a hoop and the hoop resists being inwardly compressed. In this case, the hoop is the cross-section of the body 4 of the anchor 2. The tightening force is the application of force to the body 4 by bringing wings 6 together. These hoop stresses take a substantial amount of the energy provided by moving the wings 6 together and store it in tension within the material of body 4. As a result, a seriously reduced amount of energy is available for contacting the outer surface of the catheter to cause frictional contact with the catheter to hold it in place with respect to the anchor 2.
Another problem occurs because anchor 2 is placed in a pocket 20 formed in tissue 18 in a patient""s body. A problem with this anchor 2 is that it is difficult bring the wings 6 from their 180xc2x0 opposed position to their pinched position in the small opening provided by in the pocket in the tissue 18. This problem is exacerbated when the surgeon also has to open slit 10 and place the catheter 14 in the central channel 8. This is often accomplished by bending wings 6 together on the opposite side of body 4 so that slit 10 opens. This requires a very dexterous maneuver in the small space presented by the pocket 20 in the tissue 18. Often, it takes several tries to get the catheter 14 positioned within central channel 8 through slit 10. This complicates the surgery with the concomitant chance or problems or complications.
The present invention provides an anchor for securely positioning a catheter intended to deliver drug or other medicaments to a desired position in tissue wherever found in the body or in epidural or intrathecal space of a spinal cord or brain. The present invention comprises, in the preferred embodiment, a generally tubular body for receiving the catheter and a pair of wings to assist in securing the device. The body has a slot that extends through the body between the wings. The wings and the slot cooperate so that the opposed edges of the slot just come together as the wings are brought into contact with each other. In this way, hoop forces are virtually eliminated so that all the stress produced by bringing the wings together is applied to the catheter to frictionally hold the catheter in position within the anchor. The wings interact with the slot to radially compress the catheter within the lumen of the tubular body to hold the catheter in a fixed relation to the tubular body.
In addition, the wings allow the device to be sutured to tissue to secure and fix the device to tissue. A first suture is placed around the base of the wings very near where the wings contact the body of the anchor. A second suture secures the wings together and affixes the anchor to the patient""s tissue. This suture is placed through an eyelet in each of the wings. In this way, the normal stresses applied to the catheter by bringing the wings together are maximized.
In use the catheter is placed in the central channel of the anchor. The wings are brought together and sutured. The wings are then sutured to the patient""s tissue.
It is an object of the present invention to provide an anchor that securely holds a catheter without crushing, kinking,pinching or occluding the catheter.
It is another object of the invention to provide an anchor can be securely attached to a patient""s tissue.
It is another object of the invention to provide an anchor that is easy to use.
The proposed design addresses these objects. Movement of the catheter relative to the anchor is greatly decreased because of the holding force provided as the wings are brought together and secured. Because the anchor is smaller and easier to place than known anchors, the physician should be able to place the anchor closer to the spinal entry site. This should make it unlikely that the catheter will pull out of the implant site and bunch up as the patient moves.